1. Field of the Invention
The present invention relates to a method for operating a drive unit, the drive unit having an electric machine that, in normal operation, is operated with a current provided by an inverter on at least two phases, particular phase voltages for the electric machine being set on the phases.
2. Description of Related Art
Methods of the type named above are known from the existing art. In these, the electric machine is supplied by the inverter with current present on the at least two phases. In order to set the rotational speed and torque of the electric machine, the phase voltages are set that are adjacent to the phases. However, if during normal operation of the electric machine an error occurs, in particular an error of the inverter, frequently a separating device (for example a phase separation relay, which may be electronic or electromechanical) is used to completely separate the electric machine from the inverter. In this way, the electric machine is prevented from producing a torque in an undesired direction when the error of the inverter occurs. In this regard, reference is made to published international patent application document WO 98/10971 A1. The drive unit here standardly has a device with which the occurrence of the error of the inverter can be determined. Such devices are also known from the existing art. As a general reference concerning the existing art, reference is made to published German patent application document DE 198 49 889 A1. This patent specification describes a method for regulating synchronous machines, optimized for power and efficiency. At least three regulating ranges are formed in which the regulation of an excitation current and of phase currents of an electric machine fashioned as a generator takes place according to various criteria. In this way, the available output power and the efficiency of the generator can be increased in comparison with a generator having passive diode rectification. In normal operation of the generator, the regulating ranges are selected as a function of existing requirements and boundary conditions, such as the desired output power and the existing generator rotational speed.